This article investigates the impact of the method of inoculant addition on the solidification and shrinking tendency. Commercial foundries that manufacture ductile iron castings typically employ a conventional magnesium treatment, followed by an inoculation treatment. There is a lack of comprehensive studies on examining the impact of mixing an inoculant with a magnesium alloy during the process of magnesium treatment.
In this study, an industrial gear housing hub casting is used to conduct studies comparing the shrinkage tendency of the casting when subjected to single-step inoculation versus two-step inoculation. Thermal analysis cups are poured to get the solidification cooling curves for 27 heats of castings. The analyzed solidification data is used to establish a correlation between inoculation method versus microstructure and shrinkage tendency of gear housing hub casting.
The two-stage inoculation process in ductile cast iron, comprising pre-inoculation and stream inoculation, serves as an effective approach for minimizing recalescence ΔTR and solidification angle Θ. The relationship between recalescence, solidification angle Θ and shrinkage has been developed for 27 heats of gear housing hub castings. It was observed that the number of castings exhibiting shrinkage in the respective heats increases with rising recalescence and solidification angle Θ. The recalescence ΔTR plays a crucial role in the management of shrinkage. The single-stage inoculation was performed on 27 heat samples, with the highest recorded recalescence temperature being 10 °C. The shrinkage porosity defect occurs in 18 castings at the specified recalescence temperature. In a similar manner, a two-stage inoculation process is conducted on an additional 27 samples utilizing the same heat treatment. The highest recorded recalescence during this process is 9 °C, and a shrinkage porosity defect is identified in 9 castings at this recalescence temperature.
To enhance the quantity and size distribution of nodules, thereby minimizing shrinkage in ductile cast iron, it is more beneficial to add 0.15% inoculant during magnesium treatment and then inoculate with a 0.25% transfer ladle stream. This approach differs from simply inoculating with a 0.4% stream.
